1. Field of the Invention
The present invention relates to the art of well drilling and earth boring. More particularly, the invention relates to packer devices for closing annular space between well tubing and well casing or the borehole wall.
2. Description of Related Art
Well production tubing, for example, is surrounded by an annular space between the exterior wall of the tubing and the interior wall of the well casing or borehole wall. Frequently, it is necessary to seal this annular space between upper and lower portions of the well depth. Appliances for accomplishing the sealing function are known in the well drilling arts as xe2x80x9cpackersxe2x80x9d. Traditionally, the sealing element of a packer is a ring of rubber or other elastomer that is in some manner secured and sealed to the interior well surface which may be the interior casing wall or the raw borehole wall. By compression or inflation, for example, the ring of rubber is expanded radially against the casing or borehole wall.
As an incident to the sealing function of a packer, the annular space sealing apparatus must be secured at the required position along the well length. The position securing operation is characterized in the art as xe2x80x9csettingxe2x80x9d. Packers are usually set by a mechanism known to the art as a xe2x80x9cslipxe2x80x9d. Slips are wedging devices in which a pair of ramped or tapered surfaces are mutually engaged to increase the combined dimension of radial thickness. Resultantly, a hardened surface penetration element such as serrated edges, teeth or diamond points are, by an axially directed force such as by hydraulic pressure or screw threads, pressed radially into a surrounding casing wall or borehole wall.
With but few exceptions, packer and slip devices are separately placed and engaged. Consequently, the physical size and length of a prior art tool string is long and expensive. Since each device is engaged separately, the complete engagement procedure is protracted. It is, therefore, an object of the present invention to combine the gripping and sealing elements of a downhole tool into one unit that is deployed in one procedural operation.
Another object of the present invention is a well packer unit that is shorter and requires less total movement or stroke for actuation. Shorter tool length also facilitates downhole placement and borehole navigation through tight borehole positions.
Also an object of the invention is a gripping/sealing tool having relatively few component parts that are less expensive to manufacture, require less interaction between the cooperative elements and allows an inventory reduction.
A further object of the invention is a symmetrical gripping/sealing system that may be set from either direction thereby making it possible to use many of the same components for a wireline set device (set from above) and a hydraulically set device (set from below).
Other advantages of the invention include a substantial elimination of body movement during actuation thereby permitting hydraulically set tools to be set more closely to one another without affecting the tubing or the other tools. Moreover, the invention gripping features extend substantially around the entire circumference of the tool thereby spreading the gripping forces more evenly across the casing ID and directly into the casing wall.
These and other objects of the invention are accomplished by a plurality of wicker faced slip elements that are loosely aligned around the perimeter of a cylindrical mandrel as sectors of a cylinder. Each slip element is saddle-shaped with the wicker faces on both ends and a saddle seat in between. A full-circle caging ring has an inside diameter sufficient to slide over the O.D. of a cylindrical tool mandrel. A plurality of axially oriented slots cut radially into the caging ring from the I.D. span the slip element saddle seats to loosely confine the respective slip elements. A peripheral slot from the I.D. around the middle of the caging ring accommodates a belt spring that biases the slip elements collectively against a cylindrical body surface. Full circle packer seals fitted around deformable metal base rings fit, collectively, over both ends of the slip elements. The slip element assembly is confined between two, oppositely facing ramps. One ramp is integral with to the tool body. The other ramp is advanced axially toward the fixed first ramp by a sliding push ring. The push ring is driven by an axially directed force such as hydraulic pressure or a threaded lead advance. The push ring directly engages a plurality of keys that are confined in slots to axial movement. Each key is secured to the caging ring by a threaded, set-screw type of shear fastener. The caging ring bears directly upon the saddle seat wall of each slip element. Consequently, upon initial advancement of the push ring, the entire assembly slides axially as a unit against the fixed ramp. Further advancement of the push ring slides the slip element end that is contiguous with the fixed ramp along and radially out from the fixed ramp to engage inside surface of a well casing.
Continued closure of the sliding ramp toward the fixed ramp shears the fasteners between the slip elements and the caging ring. Thereby released, the sliding ramp may advance under the other end of the slip element and wedge it radially against the casing I.D.
The slip and packer seal assembly may be retracted and recovered by a simultaneous lifting and rotation of the tool string.